1. Field of the Invention
The present invention relates to heat exchangers and fins for heat exchangers and methods for manufacturing the fins. More specifically, the invention relates to methods for easily processing fins for heat exchangers, in a form having an excellent brazing ability, and fins manufactured by these methods, and heat exchangers using such fins. Such fins may improve the performance of the heat exchangers by increasing the efficiency of heat transfer.
2. Description of Related Art
In a heat exchanger, it is known that the performance of the heat exchanger may be improved by increasing the efficiency of heat transfer by providing a fin. For example, there are methods for proving inner fins in heat transfer tubes, and methods for providing fins at positions outside of the heat transfer tubes. For instance, an outer fin may be provided at a position between adjacent tubes.
In an inner fin provided in a heat transfer tube for a heat exchanger, a fin configuration is known, in which a fin divides the inside of the tube into a plurality of small flow paths extending in the longitudinal direction of the tube.
In a heat exchanger having an inner fin with such small flow paths, and in which the heat transfer medium flowing in the heat transfer tubes is refrigerant, a differential between the temperature of refrigerant flowing in a small flow path formed at an air entrance side of the tube in the transverse direction of the tube and the temperature of air flowing outside the air entrance side of the tube, is greater than a differential between a temperature of refrigerant flowing in a small flow path formed at an air exit side of the tube in the transverse direction of the tube and a temperature of air flowing outside the air exit side of the tube. Therefore, the heat transfer performance at the air entrance side of the tube is generally better than the heat transfer performance at the air exit side of the tube. Consequently, the liquefaction and condensation of the refrigerant flowing in the small flow path located at the air entrance side of the tube is greatly accelerated. Moreover, the ratio of the liquid component of the refrigerant relative to the gaseous component increases, the specific gravity of the refrigerant also increases, and its flow velocity decreases. On the other hand, the liquefaction and condensation of the refrigerant flowing in the small flow path located at the air exit side of the tube is less accelerated. The ratio of the gaseous component of the refrigerant relative to the liquid component increases, the specific gravity of the refrigerant decreases, and its flow velocity increases. Thus, in a single heat transfer tube, a difference of heat transfer performance occurs in its transverse direction, namely, in the air flow direction, and the overall efficiency of heat transfer of the heat exchanger may be greatly reduced.
For such a problem, a method is known for forming an inner fin in such a form that the heat transfer medium flowing in a heat transfer tube may repeatedly diverge and rejoin. For example, Japanese Patent Publication No. JP-A-7-280484 (JP' 484) discloses an inner fin wherein a plurality of waving strips are arranged adjacent to each other in the transverse direction, and the adjacent waving strips are offset to each other in the longitudinal direction. As depicted in FIG. 13, in inner fin 101 disclosed in JP' 484, waving strips 102 and 103 are adjacent to each other and are connected between adjacent raised portions and between adjacent depressed portions at a connection length. Connection length is about L/2, which is about one-half of the length of one raised portion and about one-half of the length of one depressed portion. The connected portions are repeatedly formed in the longitudinal direction of inner fin 101.
In the inner fin having such a structure, because flow paths for repeating the diverging and rejoining of the flow of the heat transfer medium are formed between adjacent waving strips over the entire area in the plane direction of the inner fin, the temperature in the heat transfer tube inserted with the inner fin is made more uniform, and the overall efficiency of heat transfer of the tube may increase. Moreover, because the adjacent raised portions and the adjacent depressed portions are successively connected to each other, a brazing material may flow along the connected portions, and the brazing ability of the inner fin to the heat transfer tube may increase.
In the fin structure disclosed in JP' 484, however, because the adjacent raised portions and the adjacent depressed portions of adjacent waving portions 102 and 103 are connected over a relatively long region (i.e., over a length of about one-half of a raised portion or depressed portion), the respective waving strips may only be formed by pressing, and a rolling process capable of continuously processing to bend a material basically may not be applied to form the connected waving strips. If the connected waving strips were formed by a rolling process, the connected portions between the adjacent raised portions and the adjacent depressed portions would be pulled in the direction, in which the waving strips extend, and the waving strips would be deformed.
Further, because pressing is generally performed discretely at each unit area corresponding to a size of a press die, its productivity is much poorer when compared with that of a rolling process, in which the processing is continuously performed while rollers are rotated. Moreover, the press dies are expensive to produce.